X-ray radiation technology has been used in various fields for imaging and scanning objects. For x-ray radiation technology has been used in fields such as industry manufacturing, security, biomedical/medical, electronics, security, petro-chemical, food processing and biomedical. Typical areas of application include: quality assurance, non-destructive testing (NDT) inspection, product tampering, security inspection, pipe inspection, product malfunctions and fault analysis. Transmission techniques have been applied for imaging objects. Transmission x-ray techniques typically include a high x-ray energy output of 70 keV to 200 keV. In this technique, x-rays are applied to an object, and the x-rays having sufficient energy can penetrate through the object with certain attenuation based on the object's mass attenuation coefficient. The attenuation is dominated by the photoelectric effect, which decreases very rapidly with increasing photo energy and increases greatly with the increase of the atomic number of the scanned material.
Conventional transmission-based, two-dimensional x-ray security screening systems produce a flat two-dimensional projection of the inspected object, commonly referred to as a shadowgraph. Shadowgraphs do not provide information about the three-dimensional nature of the imaged object, which can be useful for many applications. For the purpose of security screening, it is important to be able to discern the position of objects within a container. For example, in the security screening of baggage and freight, the shape of an object and the relation of the object to other objects inside a container can be important. It would be advantageous to effectively and efficiently utilize x-ray imaging techniques for obtaining three-dimensional images of objects.
Computed tomography (CT) imaging, also known as CAT (computerized axial tomography) scanning, provides an imaging technique known as cross-sectional imaging. In CT imaging, a series of projection images of an object are obtained from different viewing angles. A three-dimensional image of the object can be reconstructed to reveal the internal structure to a certain resolution based on the projection images. CT technology is widely used for medical diagnostic testing, industrial non-destructive testing, inspection of semiconductor printed circuit boards (PCBs), explosive detection, and airport security scans.
Further, backscatter x-ray techniques based on the Compton scattering effect have been applied for imaging objects. Compton scattering cross section changes with the x-ray energy and is dependent on the atomic number of the material. The differences in scattering and absorption characteristics among different material with high and low atomic numbers or their alloys provide the means to detect these two classes of materials, nominally the organic materials with low atomic number and metal material with high atomic numbers. By collecting the x-rays scattered backwards by an object, an image of the object can be obtained.
Current backscatter systems are recordings of backscattered x-ray intensities from an object penetrated by pencil beam x-ray radiation. The incident pencil beam x-ray radiation is scanned sequentially across in the time domain. Each recording can be regarded as generating one pixel of a 2-D image of the scanned object. Therefore, in order to form an image of an object, the detector has to make hundreds to millions of snap shots at different locations of the object. This process can be time consuming. Further, this process can be difficult in acquiring images of fast moving object, and thus limiting the throughput of the backscatter inspection systems.
Many x-ray sources are filament-based x-ray tubes. For example, typical x-ray tubes comprise a cathode, an anode target, and a vacuum housing. The cathode is a negative electrode that delivers electrons towards the anode target. The anode is a positive electrode that attracts and accelerates the electrons through the electric field applied between the anode and cathode. The anode is typically made of metals such as tungsten, molybdenum, palladium, silver, and copper. When the electrons bombard the target, most of their energy is converted to thermal energy. A small portion of the energy is transformed into x-ray photons radiated from the target, forming the x-ray beam. The cathode and the anode are sealed in an evacuated chamber, which includes an x-ray transparent window typically composed of low atomic number elements such as beryllium. The time to warm up the filament to generate electrons, and therefore x-ray flux is considerable long because the filament needs to be heated up to over at least 1000° C. The warm-up time required for the x-ray tube leads to imaging constraints in applications to x-ray inspections. In particular, there is a limited ability to obtain sharp images of moving objects and to switch between different x-ray beams when using systems having long warm-up times.
It is desirable to have x-ray sources for use in inspection systems that can be used to generate images showing an accurate location and shape of an object to be scanned. Further, it is desirable to have an inspection system operable to quickly switch between different x-ray imaging sources to meet an increasing demand for precisely imaging objects with different features. It is also desirable to provide the ability to controllably adjust the gain, offset, and exposure time in inspection systems to improve image optimization under a variety of conditions. Further, it is desirable to provide the ability in inspection systems to switch between different x-ray sources x-ray beam locations.
Accordingly, in view of the above described difficulties and needs, there exists a need for improved methods, systems, and computer program products for improved systems and methods for x-ray imaging and scanning of objects.